l6o READINGS IN BIOLOGICAL SCIENCE 



One of the most obvious methods employed by the physical anthro- 

 pologist in studying human heredity is to analyze the effects of race mix- 

 ture." Here it is assumed that the traits that "show up" or persist in a cross 

 are "dominant." For example, when a long-head is crossed with a broad- 

 or short-head it is apparently the broadness or shortness that dominates; 

 similarly, nasal breadth thickness over lip thinness, and so on. But all this 

 is not genotypic (genetic constitution) it is phenotypic (physical ap- 

 pearance). We do not know the exact genetic pattern involved; we know, 

 for the most part, only what the end-result "looks like." Moreover, we are 

 observing the operation of only a dozen or so parts of thousands of pairs 

 of genes in Alan. It is this dozen or so for hair, eyes, nose, hps, skin, and 

 a few other traits, that we rely upon for stock and racial diagnosis; all the 

 others are presumably constant for all groups. 



Strandskov has given us an excellent summary of known gene distribu- 

 tion in Man.'' Color blindness is a sex-linked recessive, with gene (cb) on 

 the X-chromosome; color blindness is present when normal color vision 

 (Cb) is absent. Ability to taste the chemical phenyl thiocarbamide is an 

 autosomal recessive with (T) for tasting, (t) for non-tasting. In the A-B 

 blood groups we find inheritance by triple allelomorphs, as follows: 



Blood group Gene Combination 



AB 

 A 

 B 

 O 



In the M-N blood groups we find the following: 



Blood group Gene Combination 



MM Am hP- 



MN , A°> An 



NN A° An 



Biologically the knowledge of these few genetic patterns is important 

 because the mechanism is identical for all human beings; the inherited 

 traits cut straight across stock and race; e. g., all blood groups and their 

 genes are found in Whites, Yellows and Blacks, though in varying per- 

 centage combinations. It is possible that these combinations may have 

 some value in racial distinction, just as does skin color, etc., but as far as 

 transfusibility is concerned (allowing for blood groups) all human blood 

 is alike.^ 



6 T. W. Todd, "Entrenched Negro Physical Features," Human Biology, i ( i ) : 57- 

 69. 1929; W. M. Krogman, "The Inheritance of Non-Pathological Physical Traits in 

 Man," Eugenical News 21 (6): 139-146, Nov .-Dec, 1936. 



■^ H. H. Strandskov, "The Distribution of Human Genes," Sci. Mon., 52: 203-215, 

 March, 1941; "The Genetics of Human Population," Am. Nat., 76: 156-164, 1942. 



8 It is implied in the phrases "blood-relation" or "blood will tell" that somehow 

 blood is a carrier of familial relationship. The blood group is itself inherited, but blood, 

 per se, is not a vehicle of genetic transmission. 



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